In modern surgery, one of the most important instruments available to medical personnel is the powered surgical tool. Often this tool is in the form of a handpiece in which a motor is housed. Secured to the handpiece are cutting accessories designed for application to a surgical site to perform a specific medical procedure. For example, some powered surgical tools are designed for use with cutting accessories such as drills, burs or reamers for cutting bores into tissue or for selectively removing tissue such as bone. Other powered surgical tools are provided with saw heads. These tools are designed to be used with saw blades or blade cartridges used to separate large sections of hard and soft tissue. A wire driver is a power tool that, as its name implies, drives a wire into a patient, more particularly, a bone. Power tools are also used to perform other functions in the operating room. For example, it is known to use a power tool to mix the components that form a mass of surgical cement.
The ability to use powered surgical tools on a patient lessens the physical strain of surgeons when performing medical procedures on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.
One type of powered surgical tool that is especially popular with some physicians is the cordless, battery-operated powered surgical tool. As the name implies, this tool has a battery that serves as the power source for the motor. This eliminates the need to provide the tool with a power cord connected to an external-power source. Elimination of the power cord offers benefits over corded, powered surgical tools. Surgical personnel using this type of tool do not have to concern themselves with either sterilizing a cord so the cord can be introduced into the sterile surgical field or ensuring that, during a procedure, an unsterilized section cord is not inadvertently introduced into the surgical field. Elimination of the cord also results in the like elimination of the physical clutter and field-of-view blockage a cord brings to a surgical procedure.
One feature shared by both corded and cordless power surgical tools is the presence of a control switch or member on the tool. This member is often in the form of a biased switch, trigger or button. A number of corded and cordless surgical tools have handles similar to pistol handgrips. A tool of this shape is sometimes designed so that the control member is a trigger that is slidably mounted with respect to the handle.
Surgical power tools, unlike many other conventional power tools, have to do more than deliver relatively large amounts of power. Surgical power tools must also be compliant with government regulatory agencies and hospital operating room standards for medical surgery. Surgical power tools must be able to withstand repeated exposure to an environment that is saturated with steam and an environment that is very hot. This is because, prior to use, a powered surgical tool is autoclave sterilized. In this process, the tool is placed in a chamber where the atmosphere is saturated steam, the temperature is approximately 135° C. (or 275° F.) and the atmospheric pressure is approximately 207,000 Pa (or 30 psi). Internal components of the tool, including the conductive, electrical components of its control circuit, if left unprotected in and repeatedly exposed to this environment, can corrode or short circuit. A common solution is to have a sealed control module to enclose these internal electrical components in a welded or brazed housing. A problem exists because during the sterilization process these housings are repetitively exposed to both pressurized steam and a vacuum environment. This cyclic pressurizing and depressurizing of the control module causes the walls or panels of the module to repetitively bulge in and out. This repetitive flexure of the module walls/panels results in a fatigued failure of the weld/braze. As a consequence of this failure, steam can enter the module.
The Applicant's Assignee's U.S. Pat. No. 7,638,958, POWERED SURGICAL TOOL WITH CONTROL MODULE THAT CONTAINS A SENSOR FOR REMOTELY MONITORING THE TOOL POWER GENERATING UNIT, issued Dec. 29, 2009, and incorporated herein by reference, discloses one means for protecting the internal components of a surgical power tool from the affects of autoclave sterilization. The tool of this invention has a sealed module that houses the control circuit that regulates tool actuation. The control circuit regulates the actuation of the power generating unit of the surgical tool. The power generating unit emits a signal representative of its operating state. Inside the sealed control module shell is a sensor that monitors the signal emitted by the power generating unit. The control circuit, based on the sensor signal, regulates actuation of the power generating unit. Where the power generating unit is a motor, the signal emitted by the unit is the magnetic field that varies with rotor position. The sensor monitors the strength of this field.
U.S. Pat. No. 5,747,953 also discloses a means for protecting the internal components of a surgical tool from the affects of autoclave sterilization. The tool of this invention has a sealed module that houses the circuit that regulates tool actuation. Also internal to this module, are contactless sensors that monitor the states of externally mounted triggers. Attached to each trigger and located inside the tool housing is a magnet. Internal to the module are magnetic field sensors. Each sensor generates a varying signal as a function of the proximity of an associated one of the trigger magnets. The manual displacement of the trigger results in a like displacement, inside the tool, of the magnet. When a trigger and magnet are so displaced, the complementary sensor generates a signal that indicates the movement has occurred. Upon receipt of this signal, the control circuit generates the signal needed to allow an energization current to be applied to the motor.
The electrically conductive components of the on/off control assembly of the above tool are shielded from the supersaturated steam of the autoclave environment. When this tool is sterilized, these components are not adversely affected.
The control modules of the Applicant's Assignee's U.S. Pat. Nos. 5,747,953 and 7,638,958, both of which are incorporated herein by reference, have proven to be useful for shielding the tool control components and sensors from the effects of autoclave sterilization. However, the modules of both these patents include a housing that is essentially a shell to which a lid is brazed. During the sterilization process, the high pressure vapor imposes a significant pressure on the module housing. This force is known to press, or flex, the panels of the module shell and lid inwardly. Once the pressurized gas is removed from the chamber in which the tool is being sterilized, the gas within the module, which was compressed by the inward flexing of the panels forming the housing, flexes the panels outwardly to their initial state. This repeated in and out flexing of the housing lid weakens the braze that holds the lid to the complementary shell. This weakening of the braze joint can result in its separation. Once the braze separates, steam is able to flow into the module housing. This steam, when it condenses as water, collects on the components internal to the module. This water can corrode or short circuit the components internal to the module so as to render the module itself useless.
Moreover, even the panels of the module of Applicant's Assignee's U.S. Pat. No. 7,638,958 are formed with openings. Plural sets of contact pins extend into this module. A first set of pins function as the conductive paths over which power signals are applied to the module. A second set of conductive pins function as the conductive paths over which the control components internal to the module selectively apply energization signals to the power generating unit integral with the tool. A third set of pins are used to exchange data and control signals with components external to the module. These pins extend through openings in the module housing.
Presently, powered surgical tools utilize ceramic frits to seal the openings of the module housing through which these pins extend. Each fit extends between a pin and the internal wall of the module housing that defines the opening through which the pin extends. Often these frits are tubeshaped. These ceramic frits can withstand the rigors of autoclave sterilization. While these frits provide good seals, they are expensive to manufacture.